A duplexer is used for a wireless communication such as a mobile phone. FIG. 1 is a diagram illustrating a duplexer. A transmit filter 10 is connected between a common terminal Ant coupled to an antenna and a transmission terminal Tx. A receive filter 20 is connected between the common terminal Ant and a reception terminal Rx. The transmit filter 10 passes a signal in a transmission band, but suppresses a signal in a reception band of which a frequency is different from the frequency of the transmission band. Accordingly, the transmission signal inputted into the transmission terminal Tx passes through the transmit filter 10, and is outputted from the common terminal Ant. But the transmission signal is not outputted from the reception terminal Rx. The reception signal inputted from the reception terminal Rx passes through the receive filter 20, and is outputted from the reception terminal Rx. But the reception signal is not outputted from the transmission terminal Tx.
The transmit filter 10 and the receive filter 20 include surface acoustic wave (SAW) resonators, or film bulk acoustic wave resonators (FBAR). It is preferable that the transmit filter 10 and the receive filter 20 are hermetically sealed. Additionally, it is preferable to downsize the duplexer. For these reasons, packages such as laminated ceramic packages are used as packages for mounting the transmit filter 10 and the receive filter 20. These packages include a substrate for mounting chips such as filter chips. Foot pads for connecting the signal to the external are installed on an outer surface of the substrate. The foot pads behave as the common terminal, the transmission terminal, and the reception terminal.
Japanese Patent Laid-Open Publication No. 60-126809 discloses a capacitor of which a lower electrode and an upper electrode are polygonally-shaped, and are rotated so that they do not overlap each other. Japanese Patent Laid-Open Publication No. 60-43808 discloses a capacitor of which a lower electrode and an upper electrode are rectangular, and of which longer directions are at right angles each other. Japanese Patent Laid-Open Publication No. 2005-45099 discloses a capacitor of which a lower electrode's area is larger than an upper electrode's area.